Download Silicon photonic devices and integrated circuits

DOI 10.1515/nanoph-2013-0023 Nanophotonics 2014; 3(4-5): 215–228
Review article
Po Dong*, Young-Kai Chen, Guang-Hua Duan and David T. Neilson
Silicon photonic devices and integrated circuits
Abstract: Silicon photonic devices and integrated circuits
have undergone rapid and significant progresses during
the last decade, transitioning from research topics in universities to product development in corporations. Silicon
photonics is anticipated to be a disruptive optical technology for data communications, with applications such as
intra-chip interconnects, short-reach communications in
datacenters and supercomputers, and long-haul optical
transmissions. Bell Labs, as the research organization of
Alcatel-Lucent, a network system vendor, has an optimal
position to identify the full potential of silicon photonics both in the applications and in its technical merits.
Additionally it has demonstrated novel and improved
high-performance optical devices, and implemented
multi-function photonic integrated circuits to fulfill
various communication applications. In this paper, we
review our silicon photonic programs and main achievements during recent years. For devices, we review highperformance single-drive push-pull silicon Mach-Zehnder
modulators, hybrid silicon/III-V lasers and silicon nitrideassisted polarization rotators. For photonic circuits, we
review silicon/silicon nitride integration platforms to
implement wavelength-division multiplexing receivers
and transmitters. In addition, we show silicon photonic
circuits are well suited for dual-polarization optical coherent transmitters and receivers, geared for advanced modulation formats. We also discuss various applications in the
field of communication which may benefit from implementation in silicon photonics.
Keywords: optical communication; optical interconnect;
photonic integrated circuits; silicon photonics.
*Corresponding author: Po Dong, Bell Labs, Alcatel-Lucent,
791 Holmdel Road, Holmdel, NJ 07733, USA,
e-mail: [email protected]
Young-Kai Chen: Bell Labs, Alcatel-Lucent, 600 Mountain Avenue,
Murray Hill, NJ 07974, USA
Guang-Hua Duan: III-V Lab, a joint lab of ‘Alcatel-Lucent Bell Labs
France’, ‘Thales Research and Technology’ and ‘CEA Leti’, Campus
Polytechnique, 1, Avenue A. Fresnel, 91767 Palaiseau cedex, France
David T. Neilson: Bell Labs, Alcatel-Lucent, 791 Holmdel Road,
Holmdel, NJ 07733, USA
Edited by Chris Doerr
1 Introduction
There exist a variety of definitions as to what does or does
not constitute silicon photonics. Avoiding semantic arguments we shall simply give our practical definition of
silicon photonics, which is based on the goal of achieving
very large-scale integration (VLSI) of photonics. Therefore, we consider silicon photonics to be optical devices
and circuits, which satisfy two conditions. The first is that
silicon-core waveguides must be used in at least part of
the devices or circuits to provide compact optical devices,
which allow high-density integration. Secondly, fabrication of the devices should use whole-wafer processing or
equivalent techniques that would be allowed in a complementary metal-oxide-semiconductor (CMOS) fabrication
facility to allow large-scale low-cost manufacturability.
To illustrate we will consider some examples. Under this
definition, a planar lightwave circuit (PLC) based on silica
waveguides is not a silicon photonic device although it
may be fabricated on a silicon substrate in a CMOS fab.
Germanium photo detectors on silicon can be silicon
photonic devices as germanium can be directly grown on
silicon and be processed in a wafer scale afterwards [1]. A
hybrid laser fabricated by wafer bonding between III and
V wafers and silicon-on-insulator (SOI) wafers [2] may be
a silicon photonic device only if the bonding technique
used allows the full-wafer processing in the following fabrication steps.
The motivation for the first requirement can be illustrated by the many benefits coming from using silicon
as a waveguide core. With silicon oxide as the cladding,
silicon waveguides have an index contrast of ~2 and allow
sub-micrometer cross-sectional dimensions. Typically,
waveguide widths of ~0.5 µm and waveguide heights of
0.2–0.3 µm are employed for submicron silicon photonics. The greater width over height results in lower waveguide propagation loss since the loss mainly results from
the scattering at etched sidewalls. With this waveguide
geometry, a tight bending radius < 5 μm is permitted. The
tight bends result in extremely compact optical components and hence flexible circuit design, which are crucial
for very large-scale photonic integration. Due to the high
index contrast, silicon waveguides can also expand the
© 2014 Science Wise Publishing & De Gruyter
Unauthenticated
Download Date | 4/30/17 12:45 AM
216 P. Dong et al.: Silicon photonic devices and integrated circuits
mode sizes to a few microns to match the mode of optical
fibers by shrinking the core size, usually called inverse
tapers [3–5]. Compact grating structures which can efficiently couple the light between silicon waveguide guiding
modes to out-of-plane fiber modes, are also enabled by
the high index contrast [6–9]. In addition, because of the
large difference between waveguide width and height,
submicron silicon waveguides could have a large index
difference between the transverse-electrical (TE) and
transverse-magnetic (TM) modes. This large birefringence
can be used to make very compact and efficient polarization splitters and polarization rotators [10–14], which are
ideal for constructing polarization-diversified photonic
integrated circuits (PICs).
Wafer-scale CMOS fabrication enables silicon photonics to be a viable platform for very large-scale photonic circuits with high yield and low cost, by exploiting existing
and mature fabrication facilities and processes. The CMOS
industry has developed large-size silicon wafers with low
defect densities, which is particularly critical to achieve
large-scale photonics circuits. Silicon CMOS allows many
types of materials such as silicon oxide, silicon nitride,
germanium, and various metals. This enables feasible
process integration of various active and passive photonic
devices such as splitters, couplers, modulators, photo
detectors, and thermal phase shifters. By allowing the
integration of more optical functions on single chips, the
packaging cost can be greatly reduced.
Finally, if we are to achieve the goal of monolithic
electronic and photonic integrated circuits on silicon [15],
then the photonic device fabrication must use a compatible process. Monolithic integration of silicon PICs with
CMOS drivers leads to more complex optical functions
being practical, and with lower power consumption and
lower packaging cost. Furthermore, on-chip optical interconnects offered by integration of silicon photonics with
electronic integrated circuits (ICs) are expected to solve
the interconnect bottlenecks of modern electronic ICs.
Bell Labs, Alcatel-Lucent, has been actively involving
of the development of silicon photonic devices and circuits
for many years. In this paper, we review some of Bell Labs
major achievements in this area. The organization of this
paper is as follows. In the next section, we review applications and motivations of silicon photonics in different communication areas. In Sections 3 and 4, we review Bell Labs
developed silicon photonic devices and circuits including high-bandwidth silicon modulators, hybrid lasers,
polarization rotators/combiners/splitters, wavelengthdivision multiplexing (WDM) transmitters, WDM receivers, dual-polarization coherent transmitters and receivers.
We emphasize that this paper focuses on silicon photonic
devices and circuits from Bell Labs, rather than a comprehensive review of all work in silicon photonics.
2 Applications
Much of the work on silicon photonics has been targeted
primarily at applications in chip-level (including intrachip and inter-chip) optical interconnects, where it is
expected to solve the bottlenecks of metal electrical interconnects at high data rates. Our work focuses primarily on
the applications in telecommunications and short-reach
interconnects where optical systems are already being
used, but where there is a need for increased integration.
In this section, we discuss the applications and motivations using silicon photonics in long-haul and metro
coherent transmissions, as interconnects for routers and
switches, and as short-reach communications in datacenters and supercomputers.
2.1 L ong-haul/metro coherent optical
networks
In the past decades, the capacity of the core optic network
has been growing significantly, driven by the ubiquitous
multi-media users, vast data centers and cloud-based
applications. To meet this demand, the 100 Gb/s channel
data rate transponders are currently being deployed in
the long-haul optic fiber transport network and the per
channel rates will continue to grow to 400 Gb/s and 1 Tb/s
while expanding into metro and datacenter fiber networks
within the next decade [16, 17]. Advanced optical modulation formats, such as quadrature phase-shift keying
(QPSK), quadrature amplitude modulation (QAM), and
orthogonal frequency-division multiplexing (OFDM), in
combination with the coherent detection techniques are
used to increase the spectral efficiency [18, 19]. These
coherent techniques require the use of digital signal
processing (DSP) functionality at both the transmitter
and receiver to mitigate transmission impairments and
maximize channel capacity. These DSP functions are
realized on application specific ICs (ASICs) implemented
in advanced CMOS. In this way, more data bits can be
packed and coded into each optical channel to allow more
capacity per fiber. In particular, polarization-divisionmultiplexed QPSK (PDM-QPSK) is utilized in the current
networks for 100-Gb/s transponders. Next-generation networks may utilize even higher modulation formats, such
as 16-ary QAM (16-QAM).
Unauthenticated
Download Date | 4/30/17 12:45 AM
P. Dong et al.: Silicon photonic devices and integrated circuits 217
2.2 O
ptical interconnects for routers and
switches
Packet routing and switching are an essential part of
today’s network, enabling services and efficient sharing
of network transport resources. While router vendors have
provided increasingly large capacity routers they have not
been able to achieve reductions in power to match the
growth in capacity. Figure 1 shows the scaling over time
of the energy per bit routed, for high capacity Internet protocol (IP) routers. The energy per bit routed or switched is
falling at around 13.5% per year, less than trend observed
previously in 2006 [27]. This rate of reduction matches the
feature size reduction of silicon. This is the power scaling
10,000
Energy per bit routed (nJ)
Currently, the optoelectronic interfaces in the core
network are implemented with discrete component technologies such as InP lasers and detectors, LiNbO3 modulators and silica-based PLCs assembled together with bulk
optic elements to deliver the required performance. As
the capacity and data rate are increased at high capacity
network nodes, it will require smaller footprint, higher
optical port density, and lower power consumption.
Increased photonic integration will be required and is
expected to achieve this goal.
Silicon photonics technology has demonstrated
promising results to meet these capacity demands with
its capability for high integration level, low energy consumption and, in the near future, with embedded electronic intelligence, with integrated CMOS electronics, to
accommodate and mitigate the dynamic network environment. Examples of devices for these applications
include dual-polarization QPSK coherent receiver and
transmitter silicon PICs demonstrated at 112 Gb/s [20–22].
With its high integration level on a single chip, chip-scale
WDM modulator and receiver silicon PICs have been
demonstrated [23, 24]. A 1.6 Tb/s receiving capability
was implemented in a 40-channel WDM receive PIC with
40 Gb/s data rate per channel [23] as well as a 250 Gb/s
10-channel silicon modulator chip with a 25 Gb/s data
rate for each channel [24]. The emerging electronic-photonics co-integration [25, 26] would allow the photonic
integrated devices to be combined with the DSP functionality to facilitate capacity scaling and further introduce
electronic intelligence to the network node. This would
provide optimal adaptation to the dynamic network environment and mitigate many transmission impairments to
further enhance the stability and robustness of the core
networks and enable new architecture and applications
for cloud-based networks.
40% per year
Router efficiency
1000
100
13.5% per year
10
1
1985
1990
1995
2000
2005
2010
2015
2020
Year
Figure 1 Energy per bit routed for high capacity routers and
switches as a function of year of introduction. Two trends are
shown: 40% per year prior to the year 2000 and 13.5% per year
after. Black diamonds show commercially deployed full function
routers. The bandwidths used here are full duplex bandwidth where
as most router vendors specify capacity as half duplex.
that would be expected when an ASIC is limited by its I/O
power consumption [28].
Since energy efficiency is not scaling as rapidly as
capacity growth this leads to increasing power density
(20%/year). High power density leads to increased chip
operating temperatures, makes design more challenging
and limits the addition of features to routers. Ultimately the
largest capacity routers cannot be accommodated within
a single rack. Current router systems [29] for multi terabit
per second routing include multi rack solutions using
optical interconnects between racks. Electrical interconnects have frequency and distance dependent loss which
leads to a practical distance bandwidth product limit of
around 100 Gb/s.m [30]. Beyond this distance bandwidth
product, optical interconnects are typically used with
multimode fiber giving way to single mode fiber at around
1 Tb/s.m. This is illustrated in Figure 2 updated from Ref.
[30]. Routers and switches have both client side and internal interconnect requirements. The client side interfaces,
which will soon be 1 Tb/s per card usually, conform to
standards based interfaces, and require reaches of typically 100 m to 80 km. Even implementing 100 m reach
1 Tb/s interface using multimode fiber could require a
100 fiber pairs. Connecting large numbers of fibers results
in challenges to footprint both on the linecard boards
and faceplate density. Additionally there is a significantly
higher cost in providing multi-fiber ribbons. Therefore
there is a need for single mode fiber (SMF) interfaces
based on the kind of photonic integration that silicon photonics offers, even in the shorter reach space. Additionally
there is a need to make long haul interfaces such as those
Unauthenticated
Download Date | 4/30/17 12:45 AM
218 P. Dong et al.: Silicon photonic devices and integrated circuits
100 Gb/s
10 Gb/s
Data rate
1 Gb/s
100 Mb/s
10 Mb/s
1 Tb/s.m
1 Mb/s
100 Gb/s.m
100 kb/s
1m
10 m
100 m
1 km
10 km
10 Gb/s.m
100 km
Distance
Figure 2 Data rates and distances for commercial interconnects
updated from Ref. [30]. Data shows a practical distance bandwidth
product limit on electrical interconnects of around 100 Gb/s.m and
for multimode fiber around 1000 Gb/s.m.
described in the previous section available on router line
cards, to enable direct connection of routers to long haul
transport.
The internal interconnect requirements for routers and
switches are typically around twice the bandwidth of the
client interface, to account for redundancy and over speed
to avoid blocking, though the distances typically are less.
For rack to rack interconnect if we assume a minimum
distance of 50 m, to allow for placement and cabling, this
makes multimode fiber attractive at 2–20 Gb/s range and
single mode attractive above 20 Gb/s. With todays routers
having backplane interconnect requirements in the range
of 10–20 Tb/s this would require around a 1000 multimode fiber pairs. It is clear that if we wish to grow these
systems we need to increase the data rate per fiber, which
will require the use of SMF and the various techniques
such as WDM more commonly associated with longer
reach optical communication. Making these practical will
require increasing levels of photonic integration and so
silicon photonics is an attractive option.
2.3 Datacenters and supercomputers
Datacenters concentrate huge computational resources,
including computers, servers, storage, media and networking functions. Datacenter capacity grows both with
the increasing volume of Internet traffic and with the
additional requirements from new services. This growth
rate exceeds the rate of increase in processing power and
therefore results in an increase in the number of servers
and the footprint of the datacenter. This rapid expansion
of computing and data exchange capacity comes with an
increase in power consumption, which is becoming a very
important issue for present and future system deployment. It also results in increasing interconnect distances
within datacenters. It is thus of paramount importance to
develop more power-efficient communication solutions
for datacenters for which transmission distance of interest are ranging from several meters up to 2 km. Supercomputers continue to grow at around 80% per year [31] and
pose similar challenges to datacenters though they typically require lower latency and hence shorter distances
but with higher interconnect bandwidth density.
Today multimode parallel interconnects represent
the most cost-effective solution, and dominate this
market with the bit-rates of 1–10 Gb/s. However the
scalability of existing solutions is limited for several
reasons. First, they are making use of vertical-cavity
surface-emitting lasers (VCSELs), which are subject to
the limitations imposed to direct modulation bandwidth
in lasers. Currently available VCSEL commercial products are limited to 10 Gb/s and some research demonstrations have been made at 17 Gb/s-50 Gb/s. However,
the available link span with optimized multimode fiber,
such as OM3, is limited to about 300 m at 10 Gb/s and
70 m at 25 Gb/s. Secondly, it is very challenging to introduce WDM functionality in optical links using VCSEL
sources, as this would impose a high price premium to
VCSEL wavelength selection and complicated fiber coupling schemes for multimode fiber. While VCSEL devices
can be used with single mode fiber, this removes many
of advantages that packaging for multimode alignment
tolerances bring. Hence, present VCSEL based solutions
can only be scaled by increasing the number of fibers,
which is problematic in datacenters where running
multi fiber ribbons over long distances has significant
cost and for density of interconnect in supercomputers,
as with routers and switches.
For all these reasons, disruptive solutions taking
advantage of WDM in SMFs are being actively looked
at, with the goal of at higher transmission bit rates and
extended reaches. Photonic integration on silicon combining active devices such as lasers and modulators, and
passive building blocks, such as wavelength multiplexers, grating couplers, is widely perceived as the emerging
solution for a cost-effective and scalable communication
technology for datacenters/supercomputers.
We expect the bit rate per channel and the number
of WDM channels will continue to grow in coming years,
with the total capacity per link potentially reaching 1 Tb/s
using a 40 × 25 Gb/s system. At the same time parallel SMFs
or even fibers with multi single-mode cores can be used to
increase further the total link capacity. However there may
Unauthenticated
Download Date | 4/30/17 12:45 AM
P. Dong et al.: Silicon photonic devices and integrated circuits 219
exist several challenges to be overcome by silicon photonics before mass deployment:
1. Decrease of power consumption: this means that in
particular silicon modulators with low drive voltage
and power-efficient lasers without thermal coolers
should be developed.
2. Co-integration of electronics and photonics: high
capacity silicon PICs need to be connected with
modulator drivers, transimpedance amplifiers
(TIAs), control electronic circuits, etc. Cost-effective
co-integration scheme should be developed to allow
the exploitation of the potentials of silicon PICs.
3 Silicon photonic devices
In this section, we review a few silicon photonic devices
developed at Bell Labs. These devices include modulators,
hybrid lasers and polarization elements, which are building blocks for photonic integrated circuits.
3.1 Single-drive push-pull silicon MZMs
Electro-optic modulators are one of the most crucial
devices in optical communication. The performance of
a Mach-Zehnder modulator (MZM) can be determined
by three most important parameters, the bandwidth
(or speed), the voltage swing Vπ for a phase change of π
between the two arms of MZMs, and the insertion loss.
Among the three parameters, reducing Vπ is usually
results in reduced bandwidth and increased insertion
loss. However, for many current and future applications,
it is highly desirable to have both higher bandwidth and
lower Vπ, driven by increasing data rates, lower power
consumption, as well as difficulties to develop high-voltage amplifiers with broad bandwidths. This poses challenges for electro-optic modulators, especially for silicon
modulators, which further suffer from the weak electrooptic effect in silicon.
High-bandwidth modulation in silicon can be realized by free-carrier induced index change [32]. The
carrier-density modulation in a silicon waveguide can
be obtained with carrier injection in a forward-biased
pin diode structure [33], carrier accumulation in a MOS
capacitor structure [34], or carrier depletion in a reversebiased pn diode structure [35–40]. Carrier depletion has
the weakest modulation efficiency, yet comes with the
best high data rate performance, as doping profiles can
be used to optimize junction capacitance. Recently, high
data rates of 30–50 Gb/s have been demonstrated using
carrier depletion [35–40]. However, most of the reported
high-bandwidth silicon carrier-depletion MZMs were
demonstrated by using devices with rather short phase
shifters with an extremely high or impractical Vπ. A typical
Vπ for > 25 Gb/s operation is larger than 7 V [35–40]. Compared with LiNbO3 or InP modulators where a Vπ of 2–3 V
can be achieved, the Vπ of silicon MZMs is much higher.
In [24, 38, 41], novel single-drive push-pull MZMs
with low Vπ and high bandwidth were demonstrated by
Bell Labs. The modulation of these MZMs is based on the
carrier depletion of silicon pn junctions embedded in the
middle of silicon waveguides. A transmission-line electrode is loaded with the junction capacitor. Larger load
capacitances make it more challenging to design the travelling-wave electrodes. A single-drive push-pull scheme
can be employed to effectively reduce the capacitance
in half, where both modulator arms are symmetrically
doped and share a highly n-doped region in the center
(see Figure 3A). Symmetric coplanar strips are connected
with outside highly p-doped regions of two MZM arms.
The central highly n-doped region is connected separately
for dc bias. Since the two junction capacitors in two MZM
arms are connected in serial, the loaded capacitance on
the transmission line is half of that for one arm (assume
the capacitance are the same for both arms). This design
Figure 3 Single-drive push-pull silicon MZM [38]. (A) Waveguide
cross-section for high speed modulation. (B) Optical picture of a
fabricated MZM. (C) Optical eye diagram at 30 Gb/s for a MZM with
a Vπ of 3.1 V.
Unauthenticated
Download Date | 4/30/17 12:45 AM
220 P. Dong et al.: Silicon photonic devices and integrated circuits
allows both arms to be driven in a push-pull fashion with
a single input drive signal. Furthermore, the push-pull
scheme reduces the modulation-induced frequency chirp.
In [38], the Vπ was demonstrated to be as low as 3.1 V at
a high data rate up to 30 Gb/s and 40–50 Gb/s modulations for shorter devices with higher Vπ were also demonstrated. The achieved Vπ is close to that demonstrated for
LiNbO3 and InP modulators, however, the insertion loss
is relatively high due to free carrier induced loss from pn
junctions. In [41], the modulation chirp and dispersion
tolerance of this type of modulators were presented.
A
B
3.2 Hybrid silicon/III-V lasers
Figure 4 Hybrid silicon/III-V laser. (A) Optical picture of a bonded
III-V on silicon wafer. (B) SEM image of a hybrid silicon/III-V laser
reported in Ref. [43].
A
Bragg
reflector
Bragg
reflector
Ring
resonator R2
Heater
InP gain
section
Ring
resonator R1
Bragg grating
for vertical
light output
B
0
-10
-20
Power (dBm)
The laser source is an important building block for PICs
on silicon. Today, practical Si-based light sources are
still missing, despite the recent demonstration of a germanium laser [42]. This situation has driven research to
the heterogeneous integration of III-V semiconductors on
silicon [2]. In order to densely integrate the III-V semiconductors with the silicon waveguide circuits, mainly adhesive and molecular wafer bonding techniques are used.
In these approaches, unstructured InP dies or wafers are
bonded, epitaxial layers down, on a SOI waveguide circuit
wafer, after which the InP growth substrate is removed
and the III-V epitaxial film is processed. Figure 4A shows
a 2″ InP wafer bonded to an 8″ SOI wafer with patterned
silicon waveguide structure. Figure 4B shows a scanning
electron microscope (SEM) image of a hybrid silicon/III-V
1.9-µm laser after the III-V waveguides were fabricated on
top of silicon waveguide, reported by Dong et al. from Bell
Labs [43].
Duan et al. have developed hybrid silicon/III-V lasers
exhibiting new features [44–48]. For instance, III-V waveguides have a narrow width of < 3 µm, reducing the power
consumption of the devices. In order to make the mode
coupling efficient, both the III-V waveguide and silicon
waveguide are tapered, with a tip width for the III-V
waveguide down to 300 nm for some devices. Moreover,
a widely wavelength tunable laser was demonstrated
[44], as schematically shown on Figure 5A. This laser
consists of an InP based amplification section, tapers for
the modal transfer between III and V and Si waveguides,
two ring resonators (RRs) for single mode selection, metal
heaters on top of the rings for the thermal wavelength
tuning and Bragg gratings providing reflection and output
fiber coupling. In the silicon sections, ring resonators
1 (R1) and 2 (R2) have free spectral ranges (FSR) of 650
and 590 GHz, respectively. Figure 5B shows the superimposed laser emission spectra by changing heating power
-30
-40
-50
-60
-70
-80
1520
1530
1540
1550
1560
1570
1580
Wavelength (nm)
Figure 5 Widely tunable hybrid silicon/III-V laser [44]. (A) Schematic view of the laser cavity, and (B) super-imposed laser spectra
of the widely tunable single-mode hybrid laser.
Unauthenticated
Download Date | 4/30/17 12:45 AM
P. Dong et al.: Silicon photonic devices and integrated circuits 221
levels to the two RRs. On the backgrounds of those spectra
curves, one can observe transmission peaks created by R2
and the transmission dips created by R1. With < 400 mW
of combined power in both heaters, a high wavelength
range over 45 nm is achieved with side mode suppression
ratio higher than 40 dB [44]. It was also demonstrated that
those lasers exhibit excellent performance as local oscillator in a coherent receiver [47]. A tunable transmitter,
integrating a hybrid silicon/III-V laser and silicon MZM
was also reported [46]. The integrated transmitter exhibits 9-nm wavelength tunability by heating an intra-cavity
ring resonator, high extinction ratio from 6 to 10 dB, and
excellent bit-error ratio (BER) performance at 10 Gb/s [46].
A
TE
or
tat
Si3N4
Si
lar
Po
o
nr
tio
iza
tor
ap
d
ea
d
Mo
TM
B
3.3 On-chip polarization elements
The aforementioned submicron silicon waveguides have
very different mode fields and effective indexes for TE
and TM modes. This introduces significant challenges for
polarization-insensitive applications such as WDM receivers. Polarization-diversified circuits can solve this challenge, however, on-chip polarization elements such as
polarization rotators and polarization beam combiners/
splitters (PBC/S) are demanded. In coherent optical transmission, the generation and detection of dual-polarization
optical signals, which doubles the data capacities of fiber
transmission, also requires these polarization elements. As
discussed in Section 1, high-index-contrast silicon waveguides allow relatively easier design of polarization rotators and PBCs compared with other photonic technologies,
since the waveguide modes are inherently hybrid modes
and also the modal index/field can be controlled by the
core size. Various silicon polarization rotators have been
reported with high performance [10–14]. Both dual-layer
and single-layer waveguide structures can be employed.
In realizing these importance, high-performance
polarization rotators and PBCs were developed by Chen
et al. from Bell Labs [12]. The polarization rotator is based
on the adiabatic mode evolution as shown in Figure 6. The
structure consists of a regular silicon waveguide with an
additional silicon nitride (SiN) structure located on top of
the silicon waveguide. The device rotates the TM polarization of a silicon waveguide to its TE polarization (or vice
versa), allowing seamless integration with other siliconbased components. Shown in Figure 6A, with the first
mode adapter, the TM mode of a regular silicon waveguide
is transitioned to the TM mode of the combined structure
with both Si and SiN having the same width. The width
of the combined structure is chosen so that its TM fundamental mode has a higher index than its TE fundamental
Figure 6 SiN-assisted polarization rotator [12]. (A) Schematic 3-D
view of the device, and (B) optical modes at different sections.
mode. In the rotator section, the silicon waveguide gradually increases its width, and at the same time the SiN
waveguide gradually reduces its width and moves away
from the silicon waveguide. At the end of the rotator, the
TE fundamental mode now has a higher index than the
TM fundamental mode. If the transition is slow enough to
be adiabatic, each optical mode should maintain its mode
order during the evolution. Another mode adapter is used
here to connect the output of the polarization rotator to a
regular silicon waveguide. To achieve a PBC/S, a silicon
waveguide directional coupler can be employed. With
same gaps, the TM-mode coupling between two adjacent
waveguides can be significantly larger than that for TE.
Using this property, it is feasible to design directional couplers which have > 95% coupling efficiency for TM mode
but < 5% for TE mode. By combining PBSs with polarization rotators, Ref. [12] reported a polarization-diversified
circuit with a 1.5 dB insertion loss and > 30 dB polarization
extinction ratios over a 60-nm spectral range.
4 S
ilicon photonic integrated
circuits
Although many silicon photonic components have been
demonstrated, the performance of most individual
Unauthenticated
Download Date | 4/30/17 12:45 AM
222 P. Dong et al.: Silicon photonic devices and integrated circuits
devices is still worse than those from individually optimized devices in LiNbO3, III-V semiconductors and silica.
Nevertheless, as more optical functionality needs to be
integrated in many applications, silicon photonics could
offer a practical and flexible platform for PICs. Bell Labs
has reported various PICs, indicating that silicon photonics could find more utility in photonic integration than in
discrete devices. At receiver side, the demonstrated PICs
include various WDM receivers [23, 49–51], dual-polarization coherent receivers based on novel gratings [21, 52]
and on-chip polarization rotators [22], dual-polarization
differential-QPSK (DQPSK) receivers [53], and spacedivision multiplexing (SDM) receivers [54]. At transmitter
side, the demonstrated PICs include 10 × 25 Gb/s dense
WDM (DWDM) modulators [24], dual-polarization coherent modulators based on silicon MZMs [20], QPSK modulators based on microring modulators [55, 56], and DWDM
10-channel variable optical attenuators with multiplexers
(VOA-MUX) [57]. In this section, we review some of them.
It is to be noted that both InP and silicon PICs are very
promising in various applications, each with their own
merits and limitations. InP PICs can provide integrated
lasers, but it is challenging to integrate lasers, modulators, photo detectors and polarization elements all on
a single chip. Moreover, its yield and cost could be concerns. Silicon PICs take the advantage of CMOS foundries
with large wafers, high yield and low cost. As mentioned
earlier, silicon waveguides also have the flexibility to
implement polarization combiners and rotators, which
offers advantages on polarization diversity circuits. With
the emerging hybrid wafer-scale integration technology to
bond InP on silicon [2], it is also feasible to support integrated amplifiers and lasers.
4.1 WDM receivers
High-index-contrast silicon waveguides have many
advantages, but with a severe drawback: the effective
index is very sensitive to fabrication variations. This translates to the phase uncertainty of an optical signal propagating through the waveguide and induces significant
challenges to achieve accurate wavelength controls for
narrow-bandwidth devices such as microrings and WDM
filters. Our approach is to use SiN waveguides to reduce
the index contrast with oxide cladding. For this purpose,
a silicon/SiN integration platform has been developed to
implement various WDM PICs. The SiN is deposited on
top of silicon waveguides by low-pressure chemical vapor
deposition. By properly designing the transition tapers
between silicon and SiN waveguides, coupling loss can be
on the order of 0.1 dB. Using the same platform, polarization rotators can be realized, as explained in the previous
section.
The demonstrated WDM receivers include a polarization-insensitive two-wavelength receiver for access applications [51], a 40-channel 40 Gb/s WDM receiver [23], a
polarization-diversified DWDM receiver [49], and a monolithic diplexer [50]. For these receivers, germanium photo
detectors by epitaxial growth on silicon waveguides were
employed [58]. In Ref. [51], Chen et al. reported a polarization-insensitive two-channel receiver which utilizes a
novel polarization-insensitive SiN Mach-Zehnder interferometer (MZI) and integrated germanium photo detectors.
A fiber-to-detector polarization-dependent loss of < 0.8 dB
was demonstrated over a wide wavelength range. By
packaging the receiver chip with TIAs, sensitivities of 23.3
and 22.6 dBm for the two channels at 2.5 Gb/s were demonstrated. In Ref. [23], Chen et al. reported a 40-channel
monolithically integrated receiver PIC on silicon, which
consists of a SiN arrayed waveguide grating (AWG) with
integrated germanium photo detectors. Net responsivities
from a cleaved standard single-mode fiber to detectors of
0.15–0.22 A/W were measured, with flattened passbands
with 1-dB bandwidth over 60% of the 200-GHz channel
spacing. Single-channel operation up to 40 Gb/s was
demonstrated with a wire-bonded TIA (see Figure 7A).
This receiver, however, only works for TE mode. In Ref.
[49], Chen et al. further demonstrated a monolithically
integrated, polarization-diversified silicon receiver chip
with 10 wavelength channels at 100-GHz spacing. It
has < 1.8 dB polarization-dependent loss and zero polarization-dependent wavelength shift. On-chip polarization
rotators have been used to convert the TM component in
an optical signal to TE mode, which is demultiplexed by
the same AWG as for the TE component.
4.2 WDM transmitters
Integrating the single-drive push-pull MZMs and a SiN
AWG, Chen et al. further demonstrated a DWDM 10 × 25 Gb/s
modulator chip with a footprint of only 5 × 8 mm2 [24]. The
SiN AWG has 100-GHz channel spacing. The MZMs have a
Vπ of ~10 V. With a drive voltage of 6 V and a 3 V reverse
bias, the achieved dynamic extinction ratios are 5.6–7.2 dB
for the modulators with a total on-chip insertion loss of
about 5 dB for all ten channels. Including the coupling
loss to fibers and the AWG loss, the total insertion loss is
~18.5 dB. Figure 7B shows the chip layout and the optical
eye diagrams of all ten channels at a data rate of 25 Gb/s
after the AWG multiplexer.
Unauthenticated
Download Date | 4/30/17 12:45 AM
P. Dong et al.: Silicon photonic devices and integrated circuits 223
amplitude, one can use optical 90° hybrids, which mix
the signal and LO with four outputs, for which 0°, 90°,
180°, and 270° phase shifts between the signal and LO are
introduced. For a dual-polarization signal, a polarizationdiversified scheme is required. A generic circuit diagram
of such coherent receiver is shown in Figure 8A. Two PBSs
are used to split the signal and LO into TE and TM components. The TE (or TM) components of signal and LO
are mixed with a 90° optical hybrid, balance-detected by
four photo detectors and amplified by two TIAs, which
produce both in-phase and quadrature information of the
signal. Such coherent receivers have been realized in discrete component formats, hybrid planar lightwave circuits
with photo detectors [59–61], InP PICs [62–64], and silicon
PICs [21, 22]. Except silicon PICs, polarization diversity or
dual-polarization coherent receivers are realized by the
use of micro-optical free-space polarization rotators and
beam splitters.
In Ref. [21, 22], two types of dual-polarization coherent
receivers were demonstrated based on silicon PICs from
Bell Labs. Doerr et al. demonstrated a grating-assisted
Figure 7 WDM transmitter and receiver. (A) Schematic layout of a
silicon PIC to detector 40-channel WDM signal. The inset shows an
optical eye diagram at 40 Gb/s. (B) Schematic layout for a silicon
PIC to generate 10-channel DWDM signal. The inset shows optical
eye diagrams of all ten channels at 25 Gb/s modulation.
4.3 Coherent receivers
Optical coherent receivers, which convert the amplitude,
phase, and polarization of an optical field signal into the
electrical domain, include a number of optical components, such as polarization splitters, 90° optical hybrids
and photo detectors. These components are ideally implemented on PICs with the advantages of accurate optical
path control, compact size, and low packaging cost. The
fundamental concept for coherent detection is to measure
the product of electrical fields from a modulated signal
and a continuous-wave (CW) local oscillator (LO). Mixing
the signal and LO using a 2 × 2 coupler can do this, for
example. To suppress dc components, balanced detection is usually employed at the two outputs. With such
2 × 2 coupler, however, only one quadrature information
of the signal can be measured. Equivalently, the complex
amplitude, which consists of both magnitude and phase,
of an electrical filed cannot be extracted by a single
photo-current measurement. In order to achieve complex
Figure 8 Coherent receiver. (A) Generic circuit diagram to detect
dual-polarization optical coherent signals. (B) Optical picture of a
silicon-PIC coherent receiver using 2-D gratings as the couplers.
The inset shows the schematic view of a 2-D grating [21]. (C) Optical
picture of a silicon-PIC coherent receiver using on-chip polarization
rotators (PR) and polarization beam splitters (PBS) [22].
Unauthenticated
Download Date | 4/30/17 12:45 AM
224 P. Dong et al.: Silicon photonic devices and integrated circuits
coherent receiver PIC [21, 52], where a 2-dimensional
(2-D) grating is used for fiber coupling, polarization splitting and 50/50 power splitting. A 2-D grating coupler is
a photonic crystal that couples a wave traveling normal
to a substrate to a wave guided parallel to the substrate
(see the insect of Figure 8B). Light incident on the grating
from the vertical direction is phase-matched to waveguide
guiding modes in a certain direction at the designed wavelength and polarization. With these gratings, the TE and
TM components of signal (and LO) can be coupled and
separated into different silicon waveguides. Once coupled
in, all of the light on the chip is TE polarized. The coupled
signal and LO pass through two 90° hybrids based on
2 × 2 multi-mode interferometers (MMI) and eight photo
detectors. The principle of coherent detection is the same
as explained for Figure 8A. Using this PIC, Doerr et al.
successfully detected a 112-Gb/s PDM-QPSK signal, with
BER performance comparable to a commercial coherent
receiver [52].
In Ref. [22], Dong et al. implemented a silicon coherent receiver by integrating on-chip polarization rotators and splitters. Shown in Figure 8C, the optical signal
enters the PIC from one facet with two polarizations.
The optical LO is coupled into the Si PIC from the other
facet. Once coupled in, the signal and LO are divided into
TE and TM polarizations by two PBSs. The TE polarized
lights proceed to the 4 × 4 MMI-based 90° hybrids, whose
four outputs are detected by four germanium photo detectors on the left side of the PIC (see Figure 8C). The balance
detection between the first and fourth photo detectors
produces the in-phase TE-polarization components, and
the second and third photo detectors produces the quadrature TE-polarization components. The TM components
from the output of PBSs are converted to TE polarization
by two polarization rotators. The converted TE lights enter
the right-side 4 × 4 MMI-based 90° hybrid, which is identical to that for the TE mode. The in-phase and quadrature
in the TM-polarization components are produced with the
same balance detection scheme as those for the TE mode.
Using this PIC co-packaged with TIAs, Dong et al. successfully detected a 112-Gb/s PDM-QPSK signal and a 224-Gb/s
PDM-16-QAM signal [22].
the two MZMs outputs with a π/2 phase difference, from
which the real and imaginary components of an optical
wave can be manipulated independently. Multi-level QAM
signal can be synthesized by using parallel I/Q modulators, or by a single I/Q modulator with multi-level electrical driving signals. Figure 9A shows a circuit diagram
for a dual-polarization I/Q modulator. In order to achieve
dual polarizations, two I/Q modulators or four MZMs are
integrated together with a polarization rotator and a PBC.
Current dual-polarization I/Q modulators in long-haul
optical systems use discrete optical components such as
LiNbO3 modulators with free-space or fiber polarization
multiplexers. Integrated approaches have been demonstrated where silica or polymer PLCs are assembled with
LiNbO3 or InP modulators [65–67]. Single-polarization I/Q
modulators have been also demonstrated by monolithic
InP or GaAs PICs [68–70]. However, monolithic PICs for
dual-polarization I/Q modulators have not been achieved
in InP PICs, to the best of our knowledge.
Recently, Dong et al. presented QPSK modulation
based on nested signal-drive push-pull silicon MZMs [71].
A 50-Gb/s QPSK signal was generated with only 2.7-dB
optical signal-to-noise ratio (OSNR) penalties from the
theoretical limit at a BER of 10-3. Compared with commercial LiNbO3 I/Q modulators, there is only ~1 dB OSNR
4.4 Coherent transmitters
A coherent modulator encodes electrical signals on both
the amplitude and phase of a light wave. Such modulator is called in-phase/quadrature (I/Q) modulator or
a vector modulator. A basic I/Q modulator consists of a
pair of MZMs and a power combiner which combines
Figure 9 Coherent transmitter. (A) Generic circuit diagram to generate dual-polarization optical coherent signals. (B) Optical picture of
a fabricated dual-polarization I/Q modulator based on a monolithic
silicon PIC. (C) 224-Gb/s PDM-16QAM constellations generated by
the silicon PIC [22].
Unauthenticated
Download Date | 4/30/17 12:45 AM
P. Dong et al.: Silicon photonic devices and integrated circuits 225
penalty. This is the first successful demonstration of
advanced modulation formats using silicon MZMs. By
further integrating two I/Q modulators and an on-chip
polarization rotator and PBC, Dong et al. further implemented a monolithic single-chip dual-polarization coherent modulator to generate a 112-Gb/s PDM-QPSK [20]
and a 224-Gb/s PDM-16-QAM signal [22]. In [20], Dong
et al. showed that the integration of on-chip polarization elements introduces an additional 0.9-dB penalty
due to polarization dependent loss. To the best of our
knowledge, this PIC is the first monolithic single-chip
dual-polarization I/Q modulator, with highest photonic
integration in this particular application. Single-polarization silicon I/Q modulators were also reported from
other groups/companies with comparable performance
to those LiNbO3-based coherent modulators [72–74]. Combining the dual-polarization silicon I/Q modulators and
the silicon receiver based on on-chip polarization elements, Dong et al. reported a 2560-km SFM transmission
of a 112 Gb/s PDM-QPSK signal [75], validating the readiness of silicon PICs in optical coherent links.
High-bandwidth advanced modulation signals can
be also realized in silicon microring modulators, which
hold the promise to achieve extremely low power consumption due to their micron-meter sizes [33, 76–79].
The resonant transmission of a microring comes with
a dramatic phase change around the resonant wavelength. For single-waveguide-coupled rings, the overcoupling condition (i.e., power couplings between bus
waveguides and rings are larger than the round-trip loss
of the rings) results in a monotonic phase change from
0 to 2π across the rings’ resonant wavelengths. A proper
resonance shift can generate a π-phase change while
maintaining the same transmitted power at a prescribed
wavelength, to produce a binary phase-shift-keying
(BPSK) signal. If two BPSK ring modulators are nested
in an MZI configuration, the QPSK modulation can be
realized when there is a π/2 phase difference between
two arms. In Ref. [55, 56], Dong et al. demonstrated a
56-Gb/s QPSK modulation using nested depletion-mode
microring modulators with a ring radius of 30 μm and
a PIC size of 0.25 mm × 2.5 mm. If two polarizations are
used, 112 Gb/s can be achieved, which are suitable for
100-Gb/s channel rates.
5 Conclusions
In this paper we have reviewed recent achievements in
silicon photonic devices and integrated circuits from Bell
Labs. From its technical advantages, we believe that silicon
photonics is well suited for various applications, which
require disruptive optical technologies for high bandwidth,
high bandwidth density, energy efficient and low cost information transmission. The discussed applications include
long-haul/metro optical coherent networks, optical interconnects for routers and switches and short-reach communications in datacenters and supercomputers. Driven by
these applications, many high-performance silicon devices
and PICs have been reported from Bell Labs. Here, we have
particularly discussed single-drive push-pull silicon MZMs,
SiN-assisted polarization rotators, hybrid silicon/III-V
lasers, silicon/SiN integrated AWGs, WDM transmitters/
receivers, and dual-polarization coherent transmitters/
receivers, which are unique and important contributions
to this field from Bell Labs. While individual device fabricated in silicon photonic rarely exceed the performance of
discrete optimized components, this should not discourage the effort to integrate them as this was also the case
with early electronic integrated circuits, and the ability to
provide large-scale integration can be used to mitigate or
compensate these limitations. The demonstrated optical
functions, high data capacities and dense integration verify
silicon photonics could be a viable and powerful platform
for numerous communication applications.
Acknowledgements: We thank Christopher R. Doerr,
Long Chen, Lawrence L. Buhl, Chongjin, Xie, Xiang Liu,
S. Chandrasekhar, Nicolas K. Fontaine, Mihaela Dinu,
Peter J. Winzer, Ricardo Aroca, Yves Baeyens, Liming
Zhang, Ting-Chen Hu, Rose Kopf, Al Tate, Douglas Gill,
Mahmoud Rasras, and Mark P. Earnshaw for their significant contributions on silicon photonics programs at Bell
Labs, Martin Zirngibl, Bob Tkach, and Jeanette Fernandes
for their support, and Tsung-Yang Liow and Guo-Qiang Lo
of the Institute of Microelectronics, Singapore for silicon
photonic device fabrication.
Received June 17, 2013; accepted February 4, 2014; previously published online March 13, 2014
References
[1] Ahn D, Hong C-Y, Liu J, Giziewicz W, Beals M, Kimerling LC,
Michel J, Chen J, Kärtner FX. High performance, waveguide
integrated Ge photodetectors. Opt Express 2007;15:3916–21.
[2] Fang AW, Park H, Kuo Y-H, Jones R, Cohen O, Liang D, Raday O,
Sysak MN, Paniccia MJ, Bowers JE. Hybrid silicon evanescent
devices. Mater Today 2007;10:28–35.
Unauthenticated
Download Date | 4/30/17 12:45 AM
226 P. Dong et al.: Silicon photonic devices and integrated circuits
[3] Shoji T, Tsuchizawa T, Watanabe T, Yamada K, Morita H.
Low loss mode size converter from 0.3 μm square silicon
wire waveguides to single-mode fibers. Electron Lett
2002;38:1669–70.
[4] Almeida VR, Panepucci RR, Lipson M. Nanotaper for compact
mode conversion. Opt Lett 2003;28:1302–4.
[5] Lee KK, Lim DR, Pan D, Hoepfner C, Oh W-Y, Wada K, Kimerling
LC, Yap KP, Doan MT. Mode transformer for miniaturized optical
circuits. Opt Lett 2005;30:498–500.
[6] Taillaert D, Bogaerts W, Bienstman P, Krauss TF, Daele PV,
Moerman I, Verstuyft S, Mesel KD, Baets R. An out-of-plane
grating coupler for efficient butt-coupling between compact
planar waveguides and single-mode fibers. IEEE J Quantum
Elect 2002;38:949–55.
[7] Taillaert D, Bienstman P, Baets R. Compact efficient broadband
grating coupler for silicon-on-insulator waveguides. Opt Lett
2004;29:2749–51.
[8] Mekis A, Gloeckner S, Masini G, Narasimha A, Pinguet T,
Sahni S, Dobbelaere P. A grating-coupler-enabled CMOS
photonics platform. IEEE J Sel Top Quant Electron 2010;99:1–12.
[9] Zhou L, Li ZY, Zhu Y, Li YT, Fan ZC, Han WH, Yu YD, Yu JZ. A novel
highly efficient grating coupler with large filling factor used for
optoelectronic integration. Chinese Phys B 2010;19:124214.
[10] Fukuda H, Yamada K, Tsuchizawa T, Watanabe T, Shinojima H,
Itabashi S. Silicon photonic circuit with polarization diversity.
Opt Express 2008;16:4872–80.
[11] Zhang J, Yu M, Lo G, Kwong D. Silicon-waveguide-based mode
evolution polarization rotator. IEEE J Sel Top Quant Electron
2010;16:53–60.
[12] Chen L, Doerr CR, Chen Y-K. Compact polarization rotator
on silicon for polarization-diversified circuits. Opt Lett
2011;36:469–71.
[13] Dai D, Bowers JE. Novel concept for ultracompact polarization
splitter-rotator based on silicon nanowires. Opt Express
2011;19:10940–9.
[14] Liu L, Ding Y, Yvind K, Hvam JM. Efficient and compact TE-TM
polarization converter built on silicon-on-insulator platform
with a simple fabrication process. Opt Lett 2011;36:1059–61.
[15] Kimerling LC, Ahn D, Apsel AB, Beals M, Carothers D, Chen Y-K,
Conway T, Gill DM, Grove M, Hong C-Y, Lipson M, Liu J, Michel J,
Pan D, Patel SS, Pomerene AT, Rasras M, Sparacin DK, Tu K-Y,
White AE, Wong CW. Electronic-photonic integrated circuits on
the CMOS platform. Proc SPIE 2006;6125:6–15.
[16] Chralyvy A. Plenary paper: the coming capacity crunch. 35th
European Conference on Optical Comm., 2009;20–24.
[17] Winzer P. Beyond 100G ethernet, communications magazine.
IEEE 2010;48:26–30.
[18] Kahn J, Ho K-P. Spectral Efficiency limits and modulation/
detection techniques for DWDM systems. IEEE J Sel Top
Quantum Electron 2004;10:259–72.
[19] Shieh W, Athaudage C. Coherent optical orthogonal frequency
division multiplexing. Electron Lett 2006;42:587–9.
[20] Dong P, Xie C, Chen L, Buhl LL, Chen Y-K. 112-Gb/s monolithic
PDM-QPSK modulator in silicon. Opt Express 2012;20:B624–9.
[21] Doerr CR, Winzer PJ, Chen Y-K, Chandrasekhar S, Rasras MS,
Chen L, Liow T-Y, Ang K-W, Lo G-Q. Monolithic polarization
and phase diversity coherent receiver in silicon. J Lightwave
Technol 2010;28:520–5.
[22] Dong P, Liu X, Sethumadhavan C, Buhl LL, Aroca R, Baeyens Y,
Chen Y. 224-Gb/s PDM-16-QAM modulator and receiver
based on silicon photonic integrated circuits. In Optical Fiber
Communication Conference/National Fiber Optic Engineers
Conference 2013, (Optical Society of America, 2013), paper
PDP5C.6.
[23] Chen L, Doerr CR, Buhl L, Baeyens Y, Aroca RA. Monolithically
integrated 40-wavelength demultiplexer and photodetector
array on silicon. IEEE Photon Technol Lett 2011;23:869–71.
[24] Chen L, Doerr CR, Dong P, Chen Y. Monolithic silicon chip
with 10 modulator channels at 25 Gbps and 100-GHz spacing.
In 37th European Conference and Exposition on Optical
Communications, (Optical Society of America, 2011), paper
Th.13.A.1.
[25] Assefa S, Green WMJ, Rylyakov A, Schow C, Horst F, Vlasov YA.
Monolithic integration of silicon nanophotonics with CMOS.
Photonics Conference (IPC), 2012 IEEE 2012:626–7.
[26] Cunningham JE, Shubin I, Thacker HD, Lee J-H, Li G, Zheng X,
Lexau J, Ho R, Mitchell JG, Ying L, Yao J, Raj K, Krishnamoorthy
AV. Scaling hybrid-integration of silicon photonics in freescale
130nm to TSMC 40nm-CMOS VLSI drivers for low power
communications. Electronic Components and Technology
Conference (ECTC), 2012 IEEE 62nd, 2012:1518–1525.
[27] Neilson DT. Photonics for switching and routing. IEEE J Sel Top
Quant Electron 2006;12:669–78.
[28] Lee M-JE, Dally WJ, Farjad-Rad R, Ng H-T, Senthinathan R,
Edmondson J, Poulton J. CMOS high-speed I/Os – present
and future. Proceedings. 21st International Conference on
Computer Design, 2003;454–461.
[29] Alcatel-Lucent 7950 extensible routing system core router
family. (Accessed May 29, 2013, at http://resources.alcatellucent.com/?cid=158011).
[30] Neilson DT. Photonics for switching and routing. European
Conference on Optical Communications 2006 (ECOC
2006);24–8.
[31] Supercomputer Top 500 List (Accessed November 2012 at:
http://s.top500.org/static/lists/2012/11/TOP500_201211_
Poster.pdf).
[32] Soref RA, Bennett BR. Electrooptical effects in silicon. IEEE J
Quantum Elect 1987;23:123–9.
[33] Xu Q, Schmidt B, Pradhan S, Lipson M. Micrometre-scale
silicon electro-optic modulator. Nature 2005;435:325–7.
[34] Liu A, Jones R, Liao L, Samara D-Rubio, Rubin D, Cohen O,
Nicolaescu R, Paniccia M. A high-speed silicon optical
modulator based on a metal-oxide-semiconductor capacitor.
Nature 2004;427:615–8.
[35] Liu A, Liao L, Rubin D, Nguyen H, Ciftcioglu B, Chetrit Y,
Izhaky N, Paniccia M. High-speed optical modulation based
on carrier depletion in a silicon waveguide. Opt Express
2007;15:660–8.
[36] Thomson DJ, Gardes FY, Hu Y, Mashanovich G, Fournier M,
Grosse P, Fedeli J-M, Reed GT. High contrast 40Gbit/s optical
modulation in silicon. Opt Express 2011;19:11507–16.
[37] Gardes FY, Thomson DJ, Emerson NG, Reed GT. 40 Gb/s silicon
photonics modulator for TE and TM polarizations. Opt Express
2011;19:11804–14.
[38] Dong P, Chen L, Chen Y-K. High-speed low-voltage single-drive
push-pull silicon Mach-Zehnder modulators. Opt Express
2012;20:6163–9.
[39] Xu H, Xiao X, Li X, Hu Y, Li Z, Chu T, Yu Y, Yu J. High speed silicon
Mach-Zehnder modulator based on interleaved PN junctions.
Opt Express 2012;20:15093–9.
Unauthenticated
Download Date | 4/30/17 12:45 AM
P. Dong et al.: Silicon photonic devices and integrated circuits 227
[40] Baehr-Jones T, Ding R, Liu Y, Ayazi A, Pinguet T, Nicholas Harris C,
Streshinsky M, Lee P, Yi Zhang, Lim AE-J, Liow T-Y, Teo SH-G,
Lo G-Q, Hochberg M. Ultralow drive voltage silicon travelingwave modulator. Opt Express 2012;20:12014–20.
[41] Chen L, Dong P, Chen Y-K. Chirp and dispersion tolerance of
a single-drive push–pull silicon modulator at 28 Gb/s. IEEE
Photon Tech L 2012;24:936–8.
[42] Liu J, Sun X, Camacho-Aguilera R, Kimerling LC, Michel J.
Ge-on-Si laser operating at room temperature. Opt Lett
2010;35:679–81.
[43] Dong P, Hu T-C, Zhang L, Dinu M, Kopf R, Tate A, Buhl L, Neilson
DT, Luo X, Liow T-Y, Lo G-Q, Chen Y-K. 1.9 µm hybrid silicon/III-V
semiconductor laser. IEE Electronic Letts 2013;49:664–6.
[44] Le Liepvre A, Jany C, Accard A, Lamponi M, Poingt F, Make D,
Lelarge F, Fedeli J-M, Messaoudene S, Bordel D, Duan G-H.
Widely wavelength tunable hybrid III–V/silicon laser with
45 nm tuning range fabricated using a wafer bonding
technique. 2012 IEEE 9th International Conference on Group IV
Photonics (GFP 2012), 2012;54–56.
[45] Duan G, Fedeli J, Keyvaninia S, Thomson D. 10 Gb/s integrated
tunable hybrid III-V/Si laser and silicon mach-zehnder
modulator. In European Conference and Exhibition on Optical
Communication (Optical Society of America, 2012), paper
Tu.4.E.2.
[46] Duan G, Jany C, Le Liepvre A, Lamponi M, Accard A, Poingt F,
Make D, Lelarge F, Messaoudene S, Bordel D, Fedeli J,
Keyvaninia S, Roelkens G, Van Thourhout D, Thomson DJ,
Gardes FY, Reed GT. Integrated hybrid III–V/Si laser and
transmitter. 2012 International Conference on Indium
Phosphide and Related Materials (IPRM 2012), 2012;27–30.
[47] de Valicourt G, Leliepvre A, Vacondio F, Simonneau C, Jany C,
Accard A, Lelarge F, Lamponi M, Make D, Poingt F, Duan G,
Fedeli J, Messaoudene S, Bordel D, Lorcy L, Antona J, Bigo S.
Coherent Colorless ONU with fully tunable hybrid III-V/
silicon lasers allowing 100 Gbit/s flexible WDM/TDM access
network. In European Conference and Exhibition on Optical
Communication, (Optical Society of America, 2012), paper
Th.3.D.4.
[48] Duan G. III-V on silicon transmitters. In Optical Fiber
Communication Conference/National Fiber Optic Engineers
Conference 2013, (Optical Society of America, 2013), paper
OM3K.4.
[49] Chen L, Doerr CR, Chen Y. Polarization-diversified DWDM
receiver on silicon free of polarization-dependent wavelength
shift. In Optical Fiber Communication Conference, OSA
Technical Digest (Optical Society of America, 2012), paper
OW3G.7.
[50] Doerr CR, Chen L, Rasras MS, Chen Y-K, Weiner JS, Earnshaw
MP. Diplexer with integrated filters and photodetector in Ge–Si
using and directions in a grating coupler. IEEE Photon Tech L
2009;21:1698–700.
[51] Chen L, Buhl L, Doerr CR, Chen Y-K. Compact integrated
polarization-insensitive two-channel receiver on silicon. IEEE
Photon Tech L 2011;23:1073–5.
[52] Doerr CR, Buhl LL, Baeyens Y, Aroca R, Chandrasekhar S,
Liu X, Chen L, Chen Y-K. Packaged monolithic silicon 112-Gb/s
coherent receiver. IEEE Photon Tech L 2011;23:762–4.
[53] Doerr CR, Fontaine NK, Buhl LL. PDM-DQPSK silicon receiver
with integrated monitor and minimum number of controls. IEEE
Photon Tech L 2012;24:697–9.
[54] Doerr CR, Taunay TF. Silicon photonics core-, wavelength-,
and polarization-diversity receiver. IEEE Photon Tech L
2011;23:597–9.
[55] Dong P, Xie C, Chen L, Fontaine NK, Chen Y-K. Experimental
demonstration of microring quadrature phase-shift keying
modulators. Opt Lett 2012;37:1178–80.
[56] Dong P, Xie C, Buhl LL, Chen Y. Silicon microring modulators for
advanced modulation formats. In Optical Fiber Communication
Conference/National Fiber Optic Engineers Conference 2013,
(Optical Society of America, 2013), paper OW4J.2.
[57] Dong P, Chen L, Chen Y-K. Monolithically integrated VOA-MUX
with power monitors based on submicron silicon photonics
platform. Optical Fiber Communication Conference and
Exposition (OFC/NFOEC 2012), paper OTu2I.5.
[58] Liow T-Y, Ang K-W, Fang Q, Song J-F, Xiong Z, Yu M-B, Lo G-Q,
Kwong D-L. Silicon modulators and germanium photodetectors
on SOI: monolithic integration, compatibility, and performance
optimization. IEEE J Sel Top Quan 2010;16:307–15.
[59] Kurata Y, Nasu Y, Tamura M, Kasahara R, Aozasa S, Mizuno T,
Yokoyama H, Tsunashima S, Muramoto Y. Silica-based PLC
with heterogeneously-integrated PDs for one-chip DP-QPSK
receiver. Opt Express 2012;20:B264–9.
[60] Wang J, Kroh M, Theurer A, Zawadzki C, Schmidt D, Ludwig R,
Lauermann M, Zhang Z, Beling A, Matiss A, Schubert C,
Steffan A, Keil N, Grote N. Dual-quadrature coherent receiver
for 100G Ethernet applications based on polymer planar
lightwave circuit. Opt Express 2011;19:B166–72.
[61] Nasu Y, Mizuno T, Kasahara R, Saida T. Temperature
insensitive and ultra wideband silica-based dual polarization
optical hybrid for coherent receiver with highly symmetrical
interferometer design. Opt Express 2011;19:B112–8.
[62] Takeuchi H, Kasaya K, Kondo Y, Yasaka H, Oe K, Imamura Y.
Monolithic integrated coherent receiver on InP substrate. IEEE
Photon Tech L 1989;1:398–400.
[63] Nagarajan R, Lambert D, Kato M, Lal V, Goldfarb G, Rahn J,
Kuntz M, Pleumeekers J, Dentai A, Tsai H, Malendevich R,
Missey M, Wu K, Sun H, McNicol J, Tang J, Zhang J, Butrie T,
Nilsson A, Reffle M, Kish F, Welch D. 10 Channel, 100Gbit/s
per channel, dual polarization, coherent QPSK, monolithic
InP receiver photonic integrated circuit. In Optical Fiber
Communication Conference/National Fiber Optic Engineers
Conference 2011, paper OML7 (2011).
[64] Lu M, Park H-C, Sivananthan A, Parker JS, Bloch E, Johansson LA,
Rodwell MJW, Coldren LA. Monolithic integration of a
high-speed widely tunable optical coherent receiver. IEEE
Photon Tech L 2013;25:1077–80.
[65] Yamazaki H, Yamada T, Suzuki K, Goh T, Kaneko A, Sano A,
Yamada E, Miyamoto Y. Integrated 100-Gb/s PDM-QPSK
modulator using a hybrid assembly technique with
silica-based PLCs and LiNbO3 phase modulators. In European
Conference on Optical Communication 2008, paper Mo.3.C.1,
Sept. 2008.
[66] Sano A, Kobayashi T, Ishihara K, Masuda H, Yamamoto S, Mori K,
Yamazaki E, Yoshida E, Miyamoto Y, Yamada T, Yamazaki H.
240-Gb/s polarization-multiplexed 64-QAM modulation and
blind detection using PLC-LN hybrid integrated modulator and
digital coherent receiver. In European Conference on Optical
Communication 2009, paper PD2.2, Sept. 2009.
[67] Yamada E, Kanazawa S, Ohki A, Watanabe K, Nasu Y, Kikuchi N,
Shibata Y, Iga R, Ishii H. 112-Gb/s InP DP-QPSK modulator
Unauthenticated
Download Date | 4/30/17 12:45 AM
228 P. Dong et al.: Silicon photonic devices and integrated circuits
integrated with a silica-PLC polarization multiplexing circuit. In
Optical Fiber Communication Conference/National Fiber Optic
Engineers Conference 2012, paper PDP5A.9, 2012.
[68] Evans P, Fisher M, Malendevich R, James A, Studenkov P,
Goldfarb G, Vallaitis T, Kato M, Samra P, Corzine S, Strzelecka E,
Salvatore R, Sedgwick F, Kuntz M, Lal V, Lambert D, Dentai A,
Pavinski D, Behnia B, Bostak J, Dominic V, Nilsson A, Taylor B,
Rahn J, Sanders S, Sun H, Wu K, Pleumeekers J, Muthiah R,
Missey M, Schneider R, Stewart J, Reffle M, Butrie T,
Nagarajan R, Joyner C, Ziari M, Kish F, Welch D. Multi-channel
coherent PM-QPSK InP transmitter photonic integrated circuit
(PIC) operating At 112 Gb/s per wavelength. In Optical Fiber
Communication Conference/National Fiber Optic Engineers
Conference 2011, paper PDPC7, 2011.
[69] Korn D, Schindler PC, Stamatiadis C, O’Keefe MF,
Stampoulidis L, Schmogrow RM, Zakynthinos P, Palmer R,
Cameron N, Zhou Y, Walker RG, Kehayas E, Tomkos I,
Zimmermann L, Petermann K, Freude W, Koos C, Leuthold J.
First monolithic GaAs IQ electro-optic modulator,
demonstrated at 150 Gbit/s with 64-QAM. In Optical Fiber
Communication Conference/National Fiber Optic Engineers
Conference 2013, paper PDP5C.4, 2013.
[70] Prosyk K, Brast T, Gruner M, Hamacher M, Hoffmann D, Millett R,
Velthaus K. Tunable InP-based optical IQ modulator for 160
Gb/s. In European Conference on Optical Communication 2011,
paper Th.13.A.5, 2011.
[71] Dong P, Chen L, Xie C, Buhl LL, Chen Y-K. 50-Gb/s silicon
quadrature phase-shift keying modulator. Opt Express
2012;20:21181–6.
[72] Milivojevic B, Raabe C, Shastri A, Webster M, Metz P, Sunder S,
Chattin B, Wiese S, Dama B, Shastri K. 112Gb/s DP-QPSK
transmission over 2427km SSMF using small-size silicon
photonic IQ modulator and low-power CMOS driver. In Optical
Fiber Communication Conference/National Fiber Optic
Engineers Conference 2013, (Optical Society of America, 2013),
paper OTh1D.1.
[73] Goi K, Kusaka H, Oka A, Terada Y, Ogawa K, Liow T, Tu X, Lo G,
Kwong D. DQPSK/QPSK modulation at 40–60 Gb/s using
low-loss nested silicon mach-zehnder modulator. In Optical
Fiber Communication Conference/National Fiber Optic
Engineers Conference 2013, (Optical Society of America, 2013),
paper OW4J.4.
[74] Korn D, Palmer R, Yu H, Schindler PC, Alloatti L, Baier M,
Schmogrow R, Bogaerts W, Selvaraja SK, Lepage G,
Pantouvaki M, Wouters JMD, Verheyen P, Van Campenhout J,
Chen B, Baets R, Absil P, Dinu R, Koos C, Freude W, Leuthold J.
Silicon-organic hybrid (SOH) IQ modulator using the linear
electro-optic effect for transmitting 16QAM at 112 Gbit/s. Opt
Express 2013;21:13219–27.
[75] Dong P, Liu X, Sethumadhavan C, Buhl LL, Aroca R, Baeyens Y,
Chen Y-K. Monolithic silicon photonic circuits enable 112-Gb/s
PDM-QPSK transmission over 2560-km SSMF, ECOC’13, invited
paper We.2.B.1.
[76] Dong P, Liao S, Feng D, Liang H, Zheng D, Shafiiha R, Kung CC,
Qian W, Li G, Zheng X, A.Krishnamoorthy V, Asghari M. Low
Vpp, ultralow-energy, compact, high-speed silicon electrooptic modulator. Opt Express 2009;17:22484–90.
[77] Rosenberg JC, Green WM, Assefa S, Barwicz T, Yang M,
Shank SM, Vlasov YA. Low-power 30 Gbps silicon microring
modulator. Quantum Electronics and Laser Science Conference
(Optical Society of America, 2011), paper PDPB9.
[78] Xiao X, Xu H, Li X, Hu Y, Xiong K, Li Z, Chu T, Yu Y, Yu J. 25 Gbit/s
silicon microring modulator based on misalignment-tolerant
interleaved PN junctions. Opt Express 2012;20:2507–15.
[79] Biberman A, Timurdogan E, Zortman WA, Trotter DC,
Watts MR. Adiabatic microring modulators. In Optical Fiber
Communication Conference/National Fiber Optic Engineers
Conference 2013, (OSA, 2013), paper OW4J.1.
Unauthenticated
Download Date | 4/30/17 12:45 AM